11 mark
Carrots have different physical characteristics such as colour.
Which genetic term describes the physical characteristics of a carrot?
| ☐ | A | genotype | |
| ☐ | B | monohybrid | |
| ☐ | C | phenotype | |
| ☐ | D | heterozygous |
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3.2 Inheritance
2
3 marks
3 marksThe seeds produced by this pea plant can be round or wrinkled.
The allele for round seeds (R) is dominant to the allele for wrinkled seeds (r).
(i)
A homozygous dominant round seeded plant was crossed with a homozygous recessive wrinkled seeded plant.
Complete the Punnett square to show the genotypes of the offspring.
(1)
| r | r | |
| R | ||
| R |
(ii)
State the percentage of the offspring that will produce round seeds.
(1)
(iii)
Which scientist discovered the basis of genetic inheritance by crossing pea plants?
(1)
| ☐ | A | Charles Darwin | |
| ☐ | B | Alfred Wallace | |
| ☐ | C | Louis Leakey | |
| ☐ | D | Gregor Mendel |
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3a1 mark
1 markGregor Mendel was an Austrian monk who studied inheritance. In one of his investigations, Mendel looked at inheritance of seed colour in sweet peas.
The pea pod colours are controlled by a single gene with two alleles. The resulting phenotypes were either pea plants with yellow seeds or pea plants with green seeds.
Define the term allele.
3b3 marks
3 marksTwo heterozygous pea plants with yellow seeds were crossed as shown in the diagram above to produce the F2 generation.
(i)
Complete the Punnet square to show the genotypes that are produced in this cross.
| Yy | |||
| ............ | ............ | ||
| Yy | Y | ............ | ............ |
| y | ............ | ............ | |
(2)
(ii)
State the phenotypic ratio produced in this cross.
(1)
3c1 mark
1 markSeed colour in sweet peas is a trait determined by a single gene.
Give the term used to describe a trait which is determined by multiple genes.
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4a2 marks
2 marksThe graph shows the different blood groups of patients recorded in a hospital.
(i)
State the type of variation shown in the graph.
(1)
(ii)
Explain your answer to part (i).
(1)
4b4 marks
4 marksThe table shows different examples of variation.
Tick all the boxes that show examples of continuous variation.
| Arm length | |
| Skin colour | |
| Eye colour | |
| Height | |
| Tongue rolling | |
| Weight |
4c3 marks
3 marksVariation can be caused by mutation.
(i)
What is a mutation?
(1)
| ☐ | A | The process of taking genes from the DNA of one organism and inserting them into the DNA of another | |
| ☐ | B | The cause of continuous phenotypic variation in organisms | |
| ☐ | C | Incorrectly formed proteins which are non-functional | |
| ☐ | D | A random change in the nucleotide base sequence of DNA |
(ii)
Random mutations in the DNA of pathogenic bacteria is a global concern due to the risks for patients having treatment in hospital.
Give the reason that mutations in bacterial DNA is of particular concern.
(2)
4d4 marks
4 marksThe following is a passage relating to variation with some missing words.
In addition to new alleles which form as a result of mutation, variation is introduced into populations through other mechanisms.
The process of ___________ creates genetic variation between gametes of an individual.
Random fusion of gametes at _____________ leads to genetic variation between _______.
Phenotype is also influenced by _____________ factors such as climate, diet or lifestyle.
Complete the above sentences, using the words from the box below. You can use each word once, more than once or not at all.
| zygotes | fertilisation | genetic | meiosis |
| environmental | mitosis | gametes | embryos |
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5a2 marks
2 marksDefine the term "monohybrid inheritance" and provide an example.
5b2 marks
2 marksState the significance of a horizontal line between a male and female symbol in a family pedigree chart.
5c6 marks
6 marksTable 1 below shows a Punett square for a cross between a heterozygous tall pea plant and a homozygous recessive short pea plant.
(i)
Fill the table knowing that:
“T” represents the allele for tall plants (dominant).
“t” represents the allele for short plants (recessive).
“T” represents the allele for tall plants (dominant).
“t” represents the allele for short plants (recessive).
(4)
Table 1
| Punnett square | ||
(ii)
Using the Punnett square above, provide the genotypic and phenotypic ratios of the potential offspring.
(2)
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13 marks
3 marksA gene coding for a protein has two alleles.
Figure 1 shows the first 5 codons of an mRNA strand for these alleles.
Allele 1 – AUG CCA CAG GAG UUC
Allele 2 – AUG CCA GAG GAG UUC
Figure 1
Allele 2 has a mutation.
Figure 2 shows the key needed to predict the translated amino acid sequence of the protein.
| codon | AUG | CCA | CAG | GAG | UUC |
| amino acid | Met | Pro | Gln | Glu | Phe |
Figure 2
Explain how the mutation in allele 2 could affect the functioning of this protein.
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23 marks
Higher Tier Only
One gene can have several different alleles.
Explain why these alleles can produce proteins with different structures.
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3a2 marks
2 marksSickle cell anaemia is another example of an inherited disorder whereby the alleles that cause it are codominant.
Sickle cell anaemia affects the shape of red blood cells, causing them to be shaped like sickles or crescent moons rather than their regular round shape. This means they can become rigid or sticky, which can slow blood flow. These red blood cells die much quicker than regular-shaped red blood cells.
Suggest why someone with sickle cell anaemia feel fatigued much more quickly than someone without sickle cell anaemia.
3b3 marks
3 marksFigure 1 shows the inheritance of sickle cell anaemia in a family.
Figure 1
(i)
Sickle cell anaemia is caused by a recessive allele (b).
Explain how it is possible to tell this from Figure 1.
Explain how it is possible to tell this from Figure 1.
(1)
(ii)
A blood test shows that person 10 is a carrier for sickle cell anaemia.
Person 10 has recently married an unaffected male who is also a carrier for sickle cell anaemia.
What is the probability that their first child will have sickle cell anaemia?
(1)
(iii)
Suggest the genotype of person 6 in Figure 1.
(1)
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4a3 marks
3 marksTay-Sachs is a rare inherited disorder that stops nerves from working properly and often leads to progressive damage to and the death of cells due to a build up.of a lipid called GM2 ganglioside
In unaffected individuals, an enzyme called β-hexosaminidase A helps to break down GM2 ganglioside.
Explain how a change in one amino acid in β-hexosaminidase A could stop the enzyme working properly.
4b5 marks
5 marksTay-Sachs is caused by a recessive allele.
The diagram in Figure 1 shows the inheritance pattern for Tay-Sachs in a family.
Figure 1
(i)
State the genotypes and phenotypes of individuals 8 and 2.
Use T for the normal allele and t for Tay-Sachs disease.
Use T for the normal allele and t for Tay-Sachs disease.
(2)
(ii)
Explain your choice of genotype for individual 2.
(3)
4c6 marks
6 marksThere are few known cures for DMD, but one type of treatment currently being researched is the use of stem cell therapy. This involves using stem cells from the patient to make healthy muscle cells, which could then be used to replace the damaged ones that cause DMD. The new muscle cells have a low risk of being rejected by the patient however the gene mutation may still affect some of these stem cells.
The graph in Figure 2 shows how patients categorised their DMD symptoms following treatment by stem cell therapy.
Figure 2
(i)
Calculate the percentage decrease between patients who felt a mild improvement and patients who felt a significant improvement in their symptoms.
Give your answer to 2 decimal places.
Give your answer to 2 decimal places.
(2)
(ii)
A student concluded that individuals who have DMD should use tried and tested treatments such as hormone therapy and have physiotherapy instead of receiving stem cell therapy.
Evaluate this conclusion. Use your knowledge of using adult stem cells in medicine in your answer.
Evaluate this conclusion. Use your knowledge of using adult stem cells in medicine in your answer.
(4)
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1a5 marks
5 marksFigure 1 shows a list of key terms and definitions relating to inheritance but they are in the incorrect order.
| Key term | Definition |
| 1. Heterozygous | A. Different versions of a particular gene |
| 2. Gene | B. When two alleles of a gene are the same |
| 3. Homozygous | C. An allele that expresses its phenotype even if only one copy is present |
| 4. Recessive | D. Short lengths of DNA found on a chromosome that codes for a protein |
| 5. Allele | E. When two alleles of a gene are different |
| 6. Dominant | F. An allele whose phenotype is masked unless both copies are present |
Figure 1
(i)
Match the correct key term with the corresponding definition.
(3)
(ii)
Describe the difference between genotype and phenotype.
(2)
1b5 marks
5 marksIn humans, ear wax type has two distinct types, sticky and dry. Ear wax is an inherited trait which is controlled by a single gene. The allele for sticky ear wax (E) is dominant over the allele for dry earwax (e).
(i)
A male parent with the genotype (Ee) has sticky ear wax and a female parent has dry earwax.
State the genotype of the female parent.
(1)
(ii)
Draw a Punnett square to show the possible genotypes of the offspring.
(2)
(iii)
State what the ratio of phenotypes would be for the offspring.
(2)
1c7 marks
7 marks(i)
Explain how inheritance of biological sex is determined in humans.
(4)
(ii)
Figure 2 shows a genetic diagram.
Complete the genetic diagram to show the genotypes of the parents and any offspring
(3)
Figure 2
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2a2 marks
2 marks(i)
Describe what the term 'variation' means in the context of a population.
(1)
(ii)
State why the following phrase is incorrect.
"Variation between individuals within populations is only caused by a variation in their genes"
(1)
2b9 marks
9 marksVariation in organisms can be caused by genetic and environment factors or a combination of both.
Figure 1 shows a list of characteristics in humans.
| Characteristic | Genetic | Environment | Both |
| 1. Blood type | |||
| 2. Eye colour | |||
| 3. Scar | |||
| 4. Skin colour | |||
| 5. Weight | |||
| 6. Inherited diseases |
Figure 1
(i)
Complete Figure 1, placing a tick (✓) in the appropriate column for each example characteristic.
(3)
(ii)
Give an explanation for each of your answers in Figure 1.
(6)
2c6 marks
6 marksDescribe the differences between continuous variation and discontinuous variation.
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3a2 marks
2 marksThe Human Genome Project was an international scientific research project to determine the sequence of all the bases that make up human DNA and to identify and map all of the genes.
State two potential applications of the Human Genome Project within medicine.
3b3 marks
3 marks(i)
There is usually extensive genetic variation within a population of a species due to variations in alleles.
State how this variation arises.
(1)
(ii)
State two factors that can lead to changes in the base sequence of DNA.
(2)
3c1 mark
1 markMost mutations don't significantly affect the phenotype.
Explain why this is.
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45 marks
Haemochromatosis is a disease that occurs when iron accumulates in the liver.
A person with haemochromatosis is treated by having 0.5 dm3 of their blood removed each week.
This lowers the level of iron in their blood.
(i)
Give two safety precautions needed when blood is removed from this person.
(2)
(ii)
Haemochromatosis can be inherited.
Haemochromatosis occurs when a person inherits two copies of a recessive allele.
Figure 1 shows the inheritance of haemochromatosis in a family.
Figure 1
State and explain the genotype of female Z.
(3)
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54 marks
Sickle cell disease is a recessive genetic disorder in humans.
(i)
Two parents are heterozygous for sickle cell disease.
Complete the Punnett square to show the possible genotypes of their children.
(1)
| D | d | |
| D | ||
| d |
(ii)
State the percentage probability that their children could have sickle cell disease.
(1)
(iii)
A father with the genotype dd and a mother with the genotype DD plan to have several children.
Explain why none of their children will have sickle cell disease.
(2)
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66 marks
6 marksA karyogram is a picture of the chromosomes found in the nucleus of a single cell.
Figure 1 shows a human karyogram.
Figure 1
(i)
State two reasons why this karyogram cannot be from a gamete (sex cell).
(2)
(ii)
State the gender shown by this karyogram.
(1)
(iii)
Complete the Punnett square to show how gender is inherited.
(2)
| male gametes | |||
| female gametes |
|||
(iv)
State the probability that a child will be male.
(1)
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